It's A. y=5 because y-lines are horizontal, and x-lines are vet=rtical, and all horizontal and vertical lines are perpendicular (they create a right angle). y=5 line crosses all points that are (x,5) because the 5 in (x,5) is 5 up from the origin and x left or right. y=5 is a horizontal line that is 5 up from the origin.
